Synthetic Routes - Aliphatic Compounds

Aliphatic compounds are organic compounds without a benzene ring. Most routes pass through a few key functional groups, so it helps to learn them as a connected map.From alkanes: free-radical substitution with Cl₂ or Br₂ in UV light gives a haloalkane (as a mixture of products).From haloalkanes:
• NaOH(aq), warm → alcohol
• KCN in aqueous ethanol → nitrile (one more carbon)
• excess ethanolic NH₃ → primary amine
• KOH in ethanol, hot → alkeneFrom alkenes: HBr → bromoalkane; Br₂ → dibromoalkane; steam with H₃PO₄ catalyst → alcohol.From alcohols: acidified potassium dichromate(VI) oxidises primary alcohols to aldehydes and then carboxylic acids, and secondary alcohols to ketones; heating with concentrated H₂SO₄ or H₃PO₄ gives alkenes.From aldehydes and ketones: NaBH₄ reduces them to alcohols; KCN then dilute acid gives hydroxynitriles (one more carbon).From acids and acyl chlorides: a carboxylic acid with an alcohol and concentrated H₂SO₄ gives an ester; acyl chlorides give acids, esters, amides and N-substituted amides with water, alcohols, ammonia and amines.From nitriles: reduction with LiAlH₄ or H₂/Ni gives a primary amine.Worked example. Convert 2-bromopropane into propanone. Step 1: warm NaOH(aq) gives propan-2-ol. Step 2: acidified potassium dichromate(VI), heat, oxidises this secondary alcohol to propanone.